﻿<p>An <em>IfcSeamCurve</em> is a 3-dimensional curve that has additional representations provided by exactly two distinct pcurves describing the same curve at the two extreme ends of a closed parametric surface.</p>

<blockquote class="note">NOTE&bbsp; The `seam' on a cylinder has representations as the lines u = 0 or u = 360 degrees in parameter space.</blockquote>

<p>Figure 2 shows an instance diagram explaining the use of <em>IfcSeamCurve</em> as a boundary curve of an <em>IfcCylindricalSurface</em>.</p>
<table summary="seam curve">
<tr><td><img src="../../../figures/ifcseamcurve_01.png" alt="seam curve usage"></td>
<tr><td><p class="figure">Figure 2 &mdash; use of a seam curve bounding a cylindrical surface</p></td></tr>
</table>

<blockquote class="extDef">
NOTE&nbsp; Definition according to ISO/CD 10303-42:1992<br>
A seam curve is a type of surface curve, that is a curve on a closed parametric surface which has two distinct representations as constant parameter curves at the two extremes of the parameter range for the surface. 
</blockquote> 

<blockquote class="note">NOTE&nbsp; Entity adapted from <strong>surface_curve</strong> defined in ISO 10303-42.</blockquote>

<blockquote class="history">
HISTORY&nbsp; New entity in IFC4 Add2.
</blockquote>